what happens if you press these buttons :
https://www.edtechteam.com/blog/2014/05/workaround-to-adjust-volume-on/
You said “If I press the decrease the volume button the sound gets muted.”, but you don’t say what happens if you press increase volume…
On picture which you sent press :
Mute Mute (F8)
Decrease volume Lower the volume (F9)
Increase volume Raise the volume (F10)
Does it help?